Not sure about your specific question, but generally (obvs this is not legal advice):

Under the Electronic Communications Privacy Act, e-mail messages generally have a "protected communications status" for 180 days. Thereafter, they lose their protected status and a subpoena is all that is required for a government agency to force email providers to produce a copy. Also, email exchanges sent over company computers are considered company property and are thus accessible by management. See Holmes v. Petrovich Development Co.